# Annulus

Two concentric circles form an annulus of width 10 cm. The radius of the smaller circle is 20 cm. Calculate the content area of annulus.

Result

S =  1570.796 cm2

#### Solution:

$r_{ 2 }=20 \ \text{cm} \ \\ m=10 \ \text{cm} \ \\ r_{ 1 }=r_{ 2 }+m=20+10=30 \ \text{cm} \ \\ \ \\ S_{ 1 }=\pi \cdot \ r_{ 1 }^2=3.1416 \cdot \ 30^2 \doteq 2827.4334 \ \text{cm}^2 \ \\ S_{ 2 }=\pi \cdot \ r_{ 2 }^2=3.1416 \cdot \ 20^2 \doteq 1256.6371 \ \text{cm}^2 \ \\ \ \\ S=S_{ 1 } - S_{ 2 }=2827.4334 - 1256.6371 \doteq 1570.7963 \doteq 1570.796 \ \text{cm}^2$

Our examples were largely sent or created by pupils and students themselves. Therefore, we would be pleased if you could send us any errors you found, spelling mistakes, or rephasing the example. Thank you!

Leave us a comment of this math problem and its solution (i.e. if it is still somewhat unclear...):

Be the first to comment!

## Next similar math problems:

1. Two annuluses
The area of the annular circle formed by two circles with a common center is 100 cm2. The radius of the outer circle is equal to twice the radius of the inner circle. Determine the outside circle radius in centimeters.
2. Annulus
Calculate the area of two circles annulus k1 (S, 3 cm) and k2 (S, 5 cm).
3. Annulus
The radius of the larger circle is 8cm, the radius of smaller is 5cm. Calculate the contents of the annulus.
4. Circular lawn
Around a circular lawn area is 2 m wide sidewalk. The outer edge of the sidewalk is curb whose width is 2 m. Curbstone and the inner side of the sidewalk together form a concentric circles. Calculate the area of the circular lawn and the result round to 1
5. The terrace
Around the round pool with a diameter of 5.5 meters is a wooden terrace with a width of 130 cm. What is the area of the terrace?
Determine the radius of the circle, if its perimeter and area is the same number.
7. Circle area
Calculate the circle area with a radius of 1.2 m.
8. Flowerbed
In the park there is a large circular flowerbed with a diameter of 12 m. Jakub circulated him ten times and the smaller Vojtoseven times. How many meters each went by and how many meters did Jakub run more than Vojta?
9. Ace
The length of segment AB is 24 cm and the point M and N divided it into thirds. Calculate the circumference and area of this shape.
10. Cable
Cable consists of 8 strands, each strand consists of 12 wires with diameter d = 0.5 mm. Calculate the cross-section of the cable.
11. Sidewalk
The city park is a circular bed of flowers with a diameter of 8 meters, around it the whole length is 1 meter wide sidewalk . What is the sidewalk area?
12. Circle - simple
Calculate the area of a circle in dm2, if its circumference is 31.4 cm.
13. CD disc
A compact disc has a diameter of 11.8 cm. What is the surface area of the disc in square centimeters?
14. Lawns
Before a sports hall are two equally large rectangular lawns, each measuring 40 m and 12 m. Maintenance of 10m² lawn cost 45 CZK yearly. On each lawn is circular flowerbed with a diameter 8 meters. How much money is needed each year to take on lawn care?
15. Pipe cross section
The pipe has an outside diameter 1100 mm and the pipe wall is 100 mm thick. Calculate the cross section of this pipe.
16. Trapezium 2
Trapezium has an area of 24 square cms. How many different trapeziums can be formed ?
17. Divisible by 5
How many three-digit odd numbers divisible by 5, which are in place ten's number 3?